Normal human cell strains characterized by the properties of mesenchymal stromal cells: implications for the fundamental features of cultured cells.

Human cultured cells have been established from various normal and diseased tissues, serving as valuable in vitro cellular models. Normal cell strains play an important role in reference standards for human cells in in vitro experiments; however, they often lack essential features. In this study, 13 human cell strains derived from apparently normal three different tissues were examined to characterize their molecular signatures. Each cell strain exhibited sequence variants without any notable pathogenic mutations. Although cell strains originated from three types of tissues-lung, skin, and umbilical cord-were identified by the expression of EYA4, IGFBP3, and CXCL6, respectively, conventional cellular subtypes corresponding to in vivo tissue origins would not be applicable to the cell strains. Transcriptome analysis revealed that some key mesenchymal stromal cell (MSC) markers-NT5E, THY1, and ENG-were expressed in all 13 cell strains, implying that these cells represent immature fibroblasts possessing characteristics of MSCs. Mitochondrial DNA (mtDNA) copy number in the NB1RGB cell strain increased proportionally with the population doubling level (PDL), whereas HUC-F2 cells, which did not undergo freeze-thaw cycles, showed no change in mtDNA copy number at higher PDLs. This suggests that the influence of cryopreservation needs to be taken into account and that cultured cells can be assessed based on mtDNA copy number. Normal cell strains share common characteristics despite variations arising from human genetic diversity and tissue of origin, providing fundamental insights into cultured cells.